Nitroxide Radicals as Hydrogen Bonding Acceptors. An Infrared and EPR Study.

Franchi, Paola; Lucarini, Marco; Pedrielli, Pamela; Pedulli, Gian Franco

doi:10.1002/1439-7641(20020916)3:9<789::aid-cphc789>3.0.co;2-z

Cited by 63 publications

(43 citation statements)

References 10 publications

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“…Added water could also potentially slow k 1 and k 1 i by forming a hydrogen bond to the R 2 N–O • moiety of TEMPO, which is a moderately strong hydrogen bond acceptor 26. To test this possibility, we have explored the effect of added water on the ability of TEMPO to remove H • from (acac) 2 Ru II (py-imH)27 (acac = 2,4-pentanedioanto, py-imH = 2-(2′-pyridyl)imidazole).…”

Section: Resultsmentioning

confidence: 99%

Tuning of the Thermochemical and Kinetic Properties of Ascorbate by Its Local Environment: Solution Chemistry and Biochemical Implications

2010

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Ascorbate (Vitamin C) is a ubiquitous biological cofactor. While its aqueous solution chemistry has long been studied, many in vivo reactions of ascorbate occur in enzyme active sites or at membrane interfaces, which have varying local environments. This report shows that the rate and driving force of oxidations of two ascorbate derivatives by the TEMPO radical (2,2′-6,6′-tetramethylpiperidine-1-oxyl) in acetonitrile are very sensitive to the presence of various additives. These reactions proceed by the transfer of a proton and an electron (a hydrogen atom), as is typical of biological ascorbate reactions. The measured rate and equilibrium constants vary substantially with added water or other polar solutes in acetonitrile solutions, indicating large shifts in the reducing power of ascorbate. The correlation of rate and equilibrium constants indicates that this effect has a thermochemical origin rather than being a purely kinetic effect. This contrasts with previous examples of solvent effects on hydrogen atom transfer reactions. Potential biological implications of this apparently unique effect are discussed.

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Section: Resultsmentioning

confidence: 99%

Tuning of the Thermochemical and Kinetic Properties of Ascorbate by Its Local Environment: Solution Chemistry and Biochemical Implications

2010

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“…34 The global correlation time τ c takes into account all processes which modulate the inner-sphere dipolar interaction. These processes include electronic relaxation, chemical exchange in the complex, and rotation.…”

Section: Discussionmentioning

confidence: 99%

Relaxivity Studies on Dinitroxide and Polynitroxyl Functionalized Dendrimers: Effect of Electron Exchange and Structure on Paramagnetic Relaxation Enhancement

et al. 2003

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The 1 H NMR relaxivity of o-and p-dinitroxide-substituted phthalate esters and a series of nitroxyl-functionalized poly(propylene imine) dendrimers has been measured in acetonitrile and methanol. Studies of dinitroxide relaxivity indicate that the electron exchange rate has only a small effect on relaxivity. Outer-sphere relaxivity has been measured using benzene as a probe molecule. In studies on dendritic polynitroxides, the per-nitroxidebased outer-sphere relaxivity nearly doubles for the generation 5 nitroxyl-functionalized dendrimer as compared to a mononitroxide model. This relaxivity enhancement may be due to crowding of dendrimer surface groups in higher generation dendrimers. Water relaxivity has been measured for these polynitroxides as well, and a significant inner-sphere contribution to relaxivity is found. Dendritic polynitroxides exhibit higher per-nitroxidebased water relaxivity as compared to a mononitroxide model. This relaxivity enhancement is attributed to an increase in rotational correlation time (τ c ) for the dendritic polynitroxides.

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“…8 The formed hydrogen bonds were found to be approximately as strong as those of ethers or esters. EPR spectroscopy proved to be an attractive alternative to Fourier transform IR (FTIR) measurements.…”

Section: Basic Research 31 Hydrogen Bondsmentioning

confidence: 97%

Nitroxides: Versatile Reporters and Reactants

Zottler

Gescheidt

2011

Journal of Chemical Research

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Evelyn Zottler received her MSc degree in chemistry from the University of Technology in Graz. She participated in a student exchange project with Syracuse University, USA, where she did a research internship in the group of Prof. M. B. Sponsler. She also worked as an IAESTE trainee at the University of Edinburgh, UK, in Dr D. Uhrin's group. She spent a year as an ERASMUS student at the University of Liverpool, UK. For her diploma thesis, she has been working on interactions between metal ions and pH-sensitive imidazoline nitroxides together with Prof. G. Gescheidt at the Institute of Physical and Theoretical Chemistry in Graz.Georg Gescheidt obtained his diploma in chemistry at the Albert-Ludwigs-University in Freiburg (Germany). Then he joined the group of Prof. Fabian Gerson where he obtained his PhD in the field of radical ions and their investigation by EPR spectroscopy. After two years of editorial work at Helvetica Chimica Acta (1988-90), he returned to university life. Since 2003 he has held a chair in Physical Chemistry at the University of Technology in Graz. His research interests are the molecular basis of radical and radical ion reactions in chemistry, catalysis, biomimetic systems and material science (polymer chemistry). Short-lived species are established by magnetic-resonance methods (EPR, ENDOR, time-resolved EPR (ns time scale), CIDNP), theoretical approaches, cyclovoltammetry, and, partly, by optical spectroscopy.

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Nitroxide Radicals as Hydrogen Bonding Acceptors. An Infrared and EPR Study.

Cited by 63 publications

References 10 publications

Tuning of the Thermochemical and Kinetic Properties of Ascorbate by Its Local Environment: Solution Chemistry and Biochemical Implications

Tuning of the Thermochemical and Kinetic Properties of Ascorbate by Its Local Environment: Solution Chemistry and Biochemical Implications

Relaxivity Studies on Dinitroxide and Polynitroxyl Functionalized Dendrimers: Effect of Electron Exchange and Structure on Paramagnetic Relaxation Enhancement

Nitroxides: Versatile Reporters and Reactants

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